<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

</body>
<script>
    var num = prompt('请输入你的分数');
    console.log('num/10', num / 10);
    num = parseInt(num / 10)
    switch (num) {
        case 10:
        case 9:
            alert('A');
            break;
        case 8:
            alert('B');
            break;
        case 7:
            alert('C');
            break;
        case 6:
            alert('D');
            break;
        default:
            alert('E')
    }
</script>

</html>